Electric circuit interrupter

ABSTRACT

Discloses a circuit interrupter in which an arc is established during circuit interruption. Along the path of the arc, there is provided arc-extinguishing structure from which arc-extinguishing gas is evolved by the heat of the arc. The arc-extinguishing structure is of a material comprising tungsten trioxide, and the evolved gas comprises vapors of tungsten trioxide.

United States Patent [191 Zavitsanos et al.

[11] 3,818,165 [451 June 18, 1974 ELECTRIC CIRCUIT INTERRUPTERInventors: Peter D. Zavitsanos, Norristown; J.

' Kenneth Wittle, Berwyn, both of Pa; John E. Zlupko, Delran, N.J.

General Electric Company, Philadelphia, Pa.

Filed: Apr. 26, 1973 App]. No.: 354,538

Related U.S. Application Data Assignee:

Continuation of Ser. No. 261,266, June 9, 1972,

abandoned.

U.S. Cl. 200/144 C, 200/149 'Ai Int. Cl. H0lh 33/08 Field of Search200/144 C, 149 A, 148 C References Cited UNITED STATES PATENTS 12/1970Boersma 200/144 C 3,560,685 2/l971 Bailey. 200/147 R X 3,588,405 6/1971Bailey 200/144 C Primary Examiner -Robert S. Macon Attorney, Agent, orFirm- William Freedman; J. Wesley Haubner [57] ABSTRACT Discloses acircuit interrupter in which an arc is established during circuitinterruption. Along the path of the arc, there is providedarc-extinguishing structure from which arc-extinguishing gas is evolvedby the heat of the arc. The arc-extinguishing structure is of a materialcomprising tungsten trioxide, and the evolved gas comprises vapors oftungsten trioxide.

5 Claims, 1 Drawing Figure ELECTRIC CIRCUIT INTERRUPTER This is acontinuation of application Ser. No. 261,266, filed June 9, 1972 nowabandoned.

BACKGROUND This invention relates to an electric circuit interrupterand, more particularly, relates to a circuit interrupter of the typethat employs an electronegative gas in contact with its arc to aid inarc extinction.

Examples of such circuit interrupters are disclosed in the following US.Pat. Nos. 2,757,26l-Lingal et' al; 3,021,409-Cobine et al; and1,971,836-Strom et al.- Other prior art includes US. patents 2,066,129-Triplett, 2,285,602-McMahon and 2,358,407- McMahon.

In an alternating-current circuit, circuit interruption is typicallyeffected by establishing between a pair of spaced electrodes an arethrough which current flows until a natural current zero is reached, atwhich time a recovery voltage transient rapidly builds up across theinter-electrode space. If the inter-electrode space can withstand thisrecovery voltage transient without breakdown, interruption issuccessfully completed at this current zero. The likelihood ofsuccessfully interrupting the circuit at any given current zero dependsupon the rate at which the inter-electrode space can recover itsdielectric strength at the current zero. The higher this dielectricrate, the greater the likelihood of withstanding the recovery voltageand thus completing the interruption.

It is recognized that the dielectric recovery rate can be increased byemploying an electronegative gas, such as sulfur hexafluoride, incontact with the arc. vSuch a gas has a strong attraction for freeelectrons, which carry most of the current in the arc; and by removingthese electrons more rapidly and more completely at current zero, ahigher rate of dielectric recovery is effected.

Two properties of a gas which play an important role in determining howeffectively the free electrons will be removed from the inter-electrodespace are its electron attachment cross-section and its electronaffinity. The greater the electron attachment cross-section, the morerapidly free electrons will be attracted to and captured by the vaporspecies present; and the higher the electron affinity, the greater theforce preventing subse-' quent detachment of the captured electron andits return to a free state.

SUMMARY An object of our invention is to accelerate dielectric recoveryat current zero by making available for electron capture a vapor or gasthat has, in combination, both an exceptionally high electron afrinityand an exceptionally high electron attachment cross-section.

In carrying out our invention in one form, we provide a circuitinterrupter in which an arc is established during circuit interruption.Along the path of the arc, we provide arc-extinguishing structure fromwhich arcextinguishing gas is evolved by the heat of the arc. Thearc-extinguishing structure is of a material comprising tungstentrioxide, and the evolved gas comprises vapors of tungsten trioxide.

Both the electron affinity and electron attachment cross-section oftungsten trioxide vapors are exceptionally high, a combination ofproperties that, insofar as we are aware, has not previously beenrecognized.

BRIEF DESCRIPTION OF DRAWING For a better understanding of theinvention, reference may be had to the following description taken inconjunction with the accompanying drawing, wherein the single FIGURE isa schematic showing of a circuit interrupter embodying one form of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to thedrawing there is schematically shown a circuit interrupter of theexpulsion type. This interrupter comprises an upper electrode 10, whichis stationary, and a lower electrode 12 of rod form, which is verticallymovable into and out of engagement with stationary electrode 10. Whenthe interrupter is closed, movable electrode 12 occupies a dotted lineposition 12a where its uppermost surface engages a surface 14 of theupper electrode. Currentcan then pass through the interrupter via anupper circuit portion 16, an upper terminal 17, engaged electrodes 10and 12, a lower sliding contact 18, and a lower circuit portion 21.

When the interrupter is to be opened to interrupt the circuittherethrough, electrode 12 is driven downwardly by a suitable operatingmechanism (not shown). This rapidly moveselectrode 12 out of engagementwith electrode 10 and through its illustrated solid-line intermediateposition into a fully open position shown at 12b.

When electrodes 10 and 12 are separated while current is passingtherethrough, an arc is established there between. For confining the arcand aiding in extinguishing it, a tubular housing 20 is provided.Housing 20 has a bore 22 in which rod electrode 12 is vertically movablewith only a small annular clearance space between the bore and the rod.When the material along the bore of housing 20 is heated by the hightemperature are established between the electrodes, a portion of thismaterial vaporizes. Most of these vapors are confined in the arcingspace between the electrodes until the downwardly moving rod electrode12 approaches its solid-line position of FIG. 1. When thedownwardly-moving electrode 12 does approach its position of FIG. 1,-thebore 22 is unblocked and the aregenerated vapors are then free to flowfrom the interelectrode space via the path shown by arrows 24, thuscreating a blast action that further aids in extinguishing the are if itis still present.

In one form of our invention, the tubular housing 20 is made primarilyof a ceramic material such as alumina, aluminum silicate, or zircon, andits bore 22 is lined with a coating of tungsten trioxide (W0 suitablydeposited, as by a thermal sprayingprocess, referred to in greaterdetail hereinafter. Another suitable coating technique involves mixingthe tungsten trioxide powder with a glass frit or with a suitable bindersuch as monoaluminum phosphate, then painting this mixture onto thesurface 22, and thereafter heat treating.

To facilitate the depositing of such a coating, the housing 20 ispreferably made of two semi-cylindrical pans. These parts are firstcoated on surface 22 and then are suitably secured together (by meansnot shown) to form the tubular housing 20.

The are developed by electrode-separation vaporizes some of the tungstentrioxide lining the bore 22. The

resulting tungsten, trioxide vapors are confined under pressure in thearcing space between the electrodes until the downwardly movingelectrode 12 approaches its illustrated position, at which time thevapors are expelled from thebo're via paths 24.Tungsten trioxide vaporis exceptionally effective as an arc interrupting medium. We attributethis to the exceptionally large electron attachment cross-section oftungsten trioxide in combination with its exceptionally high electronaffinity. In this respect, both the timer of tungsten trioxide (WO andthe dimer (W09 which are the predominant species present in the vapor,have an electron attachment cross-section of about 4 X 10 cm.

This electron attachment cross-section is very high compared to theattachment cross-section of the more widely used arc-extinguishinggases. For example, sulfur hexafluoride (SF has an electron attachmentcross-section of about 2.3 X 10 cm (less than 1/10 that of the W trimerand dimer). SF a compound to which SP decomposes in the presence of anarc, has an attachment cross-section much less even than that of SP i wAnother widely used arc-extinguishing material, boric acid, decomposesin the presence of an arc to H80 and the electron attachmentcross-section of H80 is about 3 X 10 cm (only about l/lO of the W0trimer and dimer).

Turning next to electron affinity, the predominant species of thetungsten trioxide vapor to be considered from an electron affinityviewpoint are the W0 dimer and the WO monomer. These each have anelectron affinity of about 4.5 electron volts (eV) according to ourmeasurements. This electron affinity is much higher than that of SF(which has an electron afiinity of about 1.3 eV) and is appreciablyhigher than that of SE, (which has an electron affinity of about 3.4eV). Boron dioxide (B0 which is the pertinent species to be consideredfrom an electron affinity viewpoint when boric acid is used as anarc-extinguishing material, has an electron affinity of about 4.7 eV.While this too is an exceptionally high electron affinity, probably evenslightly higher than that of the tungsten trioxide dimer and monomer, itshould berecalled that the electron attachment cross-section of thepertinent species in this reaction, H80 is only about l/lO that of thepertinent tungsten trioxide species. I I

The above values of electron affinity and electron attachmentcross-section have been computed from data obtained by techniques thatinvolve electron impact by mass spectrometry, such as described, forexample, in the article by PD. Zavitsanos appearing on pages l-l3 of thebook Dynamic Mass Spectrometry, edited by 4 formed uponcontact-separation vaporizes both materials along the bore 22, thusrendering the tungsten trioxide vapor available to aid in thearc-extinguishing process by performing its strong electron-attachingaction around the time of current zero. 1

Inanother embodiment of our invention, powdered tungsten trioxide, heldtogether with a suitable binder,

e. g., methyl methacrylate, islused to form a plurality of annularcakes. A stack of these cakes is pressed into the bore of an insulatingtube to form a housing corresponding to the illustrated housing 20. Anexample of this general type of construction is shown in U.S. Pat.

No. 1,971,836-Str0m et al.

Price and Williams, and published in 1969 by Heyden and Sadler of NewYork, N.Y. and London, England. It is perhaps noteworthy that Jensen andMiller, using a different and, we believe, less accurate techniqueinvolving a starting material of tungstic acid, have estimated theelectron affinity of the monomer of tungsten trioxide to be between 3.16and 3.6 eV. This work is described in an article appearing in theJournal of Chemical Physics, Vol. 52, page 3287, 1970. No mention ismade in this article of the high electron attachment cross-section oftungsten trioxide.

In another embodiment of our invention, the tungsten trioxide isincorporated in a suitable resin such as methyl methacrylate and the,entire housing 20 is molded from such mixture. In this embodiment, theare In still another embodiment of our invention, tungsten trioxide isdeposited on the fins and sidewalls of an arc chute of the type shown inU.S. Pat. No. 3,560,685- Bailey et al. or in copending application Ser.No. 162,34l-Frind et al, filed July 14, 1971, both assigned to theassignee of the present invention. In that application, an adherentcoating of fused silica is deposited by plasma-arc-spraying onto thefins and sidewalls. We use generally the same technique for depositingthe tungsten trioxide. More specifically, tungsten trioxide, in

powdered form, is fed into the spray gun where it is melted by the hotplasma stream present and converted into molten particles, which'areejected through a suitable nozzle in the plasma stream. The plasmastream containing'the molten particles is projected onto the arc chutesurface, where the particles, upon impact, flatten and freeze into-anadherent coating.

Another suitable technique for spraying the tungsten trioxide particlesis the oxy-acetylene flame spraying technique referred to in U.S. Pat.No. 3,009,041- Zlupko. The are chute shown in the Zlupko patent can alsoadvantageously have its arc-exposed splitter plates and sidewalls coatedwith tungsten trioxide.

Either of the thermal spraying techniques referred to hereinabove can beused for depositing the tungsten trioxide coating on the bore 22 of thetubular housing 20 of the drawing.

In still another'embodiment of our invention, tungsten trioxide is usedto coat the metal plates of a metal plate arc-chute such as shown inU.S. Pat. No. 3,641,293-Armitage etal. The tungsten trioxide is ap pliedin any suitable manner as by thermal spraying or by incorporating it ina ceramic cement or other vehicle, which is brushed on each plate.

While we have shown and described particular embodiments of ourinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from ourinvention in its broader aspects; and we, therefore, intend herein tocover all such changes and modifications as fall within the true spiritand scope of ourinvention.

What we claim as new and desire to secure by Letters 6 move duringinterruption, said plates having a covering thereon of a materialcomprising tungsten trioxide from which tungsten trioxide vapors areevolved during interruption.

5. The circuit interrupter of claim 1 in which said pair of electrodesare separable electrodes between which said are is established uponseparation of said electrodes and said are is adapted to move againstsaid arcextinguishing structure and evolve tungsten trioxide vaporstherefrom.

2. The circuit interrupter of claim 1 in which said arc-extinguishingstructure comprises tubular structure having a bore in which said arc islocated during interruption, said bore being lined with a materialcomprising tungsten trioxide.
 3. A circuit interrupter as defined inclaim 1 in which said circuit interrupter is an arc chute comprisingarc-extinguishing structure against which said arc is adapted to moveand evolve tungsten trioxide.
 4. A circuit interrupter as defined inclaim 1 comprising transverse plates against which the arc is adapted tomove during interruption, said plates having a covering thereon of amaterial comprising tungsten trioxide from which tungsten trioxidevapors are evolved during interruption.
 5. The circuit interrupter ofclaim 1 in which said pair of electrodes are separable electrodesbetween which said arc is established upon separation of said electrodesand said arc is adapted to move against said arc-extinguishing structureand evolve tungsten trioxide vapors therefrom.